The present invention relates to visual landing aid systems for guidance of aircraft, and more particularly to an improved electro-optical display system for enhancing visual cueing information remotely presented to a pilot during an aircraft landing approach.
Successful aircraft landings, particularly those aboard aircraft carriers, necessitate the highest degree of safety and control to insure maximum protection for personnel and equipment. In seeking to provide that degree of safety and control, visual landing aid systems have been generally used to guide the pilots of aircraft in their descent approach to aircraft carriers. One such visual landing aid system is the Fresnel Lens Optical Landing System (FLOLS) which provides primary glideslope displacement information to the pilot from the carrier deck. The FLOLS consists of a plurality of light sources situated behind a respective number, typically five, of vertically-stacked Fresnel lenses disposed between two horizontal ligh arrays, commonly known as datum bars. The array of lenses and lights provides a virtual image, as may be seen in FIG. 1, which appears to the pilot as a single light located some distance, typically about 150 feet, behind the datum bars. This single light, known as the meatball, is visible to the pilot through the center lens when he is within 9.5 minutes of arc of the desired glideslope, and is then seen as level with the datum bars. As the aircraft moves more than 9.5 minutes of arc above or below the glideslope, the meatball is seen through higher or lower Fresnel lenses, respectively, to give the appearance of moving vertically above or below the level of the datum bars so that the pilot may take corrective action to return the aircraft to the desired glideslope.
While the displacement information provided by the FLOLS has been valuable in providing feedback of relative aircraft position for glideslope control and guidance, the system has been somewhat less then optimum, having a limited capability, by inherent design, of indicating magnitude and direction of aircraft movement. Because the information provided by the FLOLS is of zero-order (displacement only), there are substantial time-lags between incorrect control inputs and the subsequent error information from the FLOLS. For example, relatively large changes in the descent rate of the aircraft can and do occur before meatball displacement on the Fresnel lens is perceived by the pilot. Furthermore, the inherent limitations of the FLOLS are compounded during night carrier landings, when there is a severe reduction in the natural visual cues used by the pilot to assist in azimuth and elevation estimation. The nightime reduction in these natural visual cues, such as expansion pattern relationships, surface texture gradients, peripheral streaming, and horizontal field-of-view discrimination, adversely affects the pilot's perceptual domain thereby rendering accurate control of azimuth and elevation far more difficult than during daylight operations and significantly increasing the risks of carrier landing accidents.